1. Field of the Invention
The present invention relates to an optical receptacle and a method for manufacturing the same. More particularly, the present invention relates to an optical receptacle which is applied advantageously to connecting parts between a device having incorporated therein an input or output circuit, such as an ONU (optical network unit) module, and an optical fiber connector plug fitted to an outer optical cord as well as to a method for manufacturing the same.
2. Description of Related Art
Optical connectors which are used for connecting optical fibers include IEC 1754-4 "Type SC Connector Family" prescribed in "JIS C-5973" (1990). This connector is generally called "SC-type optical fiber connector" and used widely in optical transmission systems. At their input and output portions for inputting and outputting optical signals, SC type optical fiber connectors couples detachably optical devices such as photo diodes (hereafter, sometimes referred to as "PD") or laser diodes (hereafter, sometimes referred to as "LD") with optical fibers. optical receptacles are optical components which connect the optical connectors with optical fiber connector plugs that are fitted on one hand to a device having input and output circuits for optical signals and on the other hand. to an optical fiber connector plug.
FIG. 1 shows schematically a conventional "SC-type optical receptacle". As shown in FIG. 1, a conventional optical receptacle 101 has an interface equivalent to an adapter in SC-type optical connectors. A housing 102 includes a substrate 107, to which a precision sleeve 103 is fixed, and a hook portion 104 and an outer shell 106. From a terminal end of the housing 102 are inserted a lens 108 and an optical element 109 such as PD or LD.
In the case of the above-described conventional optical receptacle, the lens 108 and the optical element 109 are arranged coaxially with the center axis of the precision sleeve 103 so that the optical axis of an optical fiber is aligned to that of the element to which the optical fiber is to be connected. When a single mode optical fiber is used, not only high precision alignment with the precision sleeve 103, the optical element 109 and so on is required but also the precision sleeve 103 itself must be fabricated with high precision, thus increasing the manufacturing cost of the optical receptacle.
On the other hand, it is sometimes the case that optical elements can be coupled with satisfactory working efficiency through fibers fitted to the optical elements in advance. In the case where an optical fiber is to be connected to an optical waveguide instead of an optical element itself, it is difficult to attach an optical receptacle directly to an end surface of the optical waveguide.
In order to connect a pig-tail optical fiber, which is fitted to an optical circuit, to an optical cord detachably, it is advantageous to attach an optical connector to each optical fiber and connect the fibers through an adapter since this approach is most excellent in workability and gives good connection characteristics.
As such an optical connector, there can be used widely the above-described SC-type optical fiber connectors.
FIG. 2 is a partial cross sectional view showing a conventional SC-type optical fiber connector. FIG. 3 is an exploded view of a conventional SC-type optical fiber connector adapter and a conventional SC-type optical fiber connector plug, corresponding to the part A shown in FIG. 2.
As shown in FIG. 2, input and output portions of an optical module can be fabricated, for example, by attaching, to a tip portion of an optical fiber pigtail, an SC-type optical fiber connector 202 and connecting the SC-type optical fiber connector 208 to an SC-type optical fiber adapter 203 which is fitted to a panel portion of the optical module (not shown). In this case, the SC-type optical fiber adapter 203 has two housings 204 within each of which a sleeve 205 and hooks 206 are provided. In the sleeve 205 which is fitted in the housing 204 is held a split sleeve 211 as shown in FIG. 3. The optical fiber connector 208 includes the coupling device 202 one end of which can be fitted in the SC-type optical fiber adapter 203 and the other end thereof is inserted an outer shell 212. A ferrule 209 is pressed into the outer shell by a spring 213 which is supported by an inner shell 214 over which a crimp ring 215 covers. The crimp ring 215 together with an intervening ring 216 are contained in a boot 217, which is connected to the tension member and coating of an optical fiber cord 201. The outer shell 212, the ferrule 209, the spring 213, the inner shell 214, the crimp ring 215, the ring 216 are coaxially aligned and contained within the inner cavity of the coupling device 202.
Connection to an optical fiber cable outside the optical module can be achieved by engaging the optical fiber connector plug 208 in the housing 204 such that the ferrule 209 is inserted in a split sleeve 211 and the housing 210 of the plug 208 to is clamped by the hooks 206 so that the plug 208, is prevented from rearward movement and thus does not come out of the housing 204.
As described above, the SC-type optical fiber connector shown in FIG. 2 is of a dual engagement structure. More particularly, the ferrule 209 floats within the cavity of the plug housing 210. The plug housing 210 and the sleeve 205 engage with each other. On the other hand, the ferrule 209 and the split sleeve 211 engage with each other. The sleeve 205 and the split sleeve 211 engage with the respective counterparts independently of each other. Due to this dual engagement, the SC-type optical fiber connector is resistant to tension or bending urged to the optical cord from outside. If such an outer force is applied to the connector, the connector is given substantially no adverse effect on its connecting characteristics. As shown in FIG. 3, the conventional SC-type optical fiber adapter and the SC-type optical fiber connector plug together comprise thirteen (13) components. The SC-type optical fiber connector plug is prescribed
As is well known, SC-type optical fiber connectors are used under various conditions. For example, in some applications, the optical cord receives no outer force inside the optical module to which it is connected. Therefore, in such an environment where no outer force is urged, it is wasteful to use the above-described SC-type optical fiber connector. Much less, the use of SC-type optical fiber connectors is disadvantageous in view of production costs, space required for fitting it.